Preheat the oven to 350°F.
Add milk, onion, bay leaf, and cloves to a saucepan and warm.
Meanwhile make the roux. Melt the butter in a small pan, remove from heat, and whisk in the flour. Remove the onion from the milk and whisk in the roux. Keep whisking until you have a thick white sauce without any lumps. Set aside.
Clean and remove the bottom root from the leek. Slice in half lengthwise and then into half-moons. In a clean skillet, heat some olive oil over medium-high heat until very hot. Add the leeks, it should sizzle and crackle when the leeks hit the pan. Season with salt and pepper, to taste.
Add the spinach to the leeks and season with salt. Place the garlic on the end of a fork and use it to gently toss the spinach and leeks giving it that nice garlic flavor. Once the spinach is wilted transfer to a bowl that has a colander inside and squeeze out the excess liquid.
Grease a lasagna pan or casserole dish with butter. Spoon a little béchamel on the bottom of the pan and add the sheets of pasta overlapping and filling in the bottom of the pan. Add some more béchamel over the sheets. Next, spread some of the spinach and leek mixture over the sauce and then add some of the smoked salmon. Now sprinkle some of the fresh dill on top. Spoon some more of the béchamel sauce the dill.
Just take a spoon and drizzle the sauce over the layers. You do not have to have the layer covered. It will all merge and come together in the baking process.
Season with freshly grind black pepper and cover with a third of the cheese. Spoon some béchamel sauce on top. Repeat the process starting with the pasta sheets and ending with the béchamel sauce. Add another layer of pasta sheets, béchamel and the rest of the cheese.
Place the lasagna into the oven and bake 45 minutes. Let cool for 15 minutes before cutting. Garnish with fresh chopped dill and serve immediately.